Turbocharger systems increase the power and efficiency of internal combustion engines by providing the engine with intake fluid at higher than atmospheric pressure. Conventional turbocharger systems include a turbine driven by exhaust energy from the engine, and a compressor driven by the turbine. The compressor pressurizes fluid, previously at or near atmospheric pressure, for travel through a throttle valve and aftercooler and into an engine intake manifold.
Several problems have been experienced with previously known turbocharger configurations. For example, turbochargers generally take some time to gain speed and provide increased pressure when increased power demands are placed on the system. This generally is the result of rotational inertia of the turbocharger. Therefore, when the engine is operating under transient conditions that require a quick increase in power, a delay period occurs while the turbocharger accelerates, preventing the desired instantaneous increase in power. This also holds true when the engine is operating under conditions that require quick decreases in power and pressure.
One solution that has been employed to reduce such time lag is maintaining a reserve of pressurized air (“boost”) upstream of the throttle valve. This reserve of pressurized air may be released when increased power demands require a rapid increase of inlet air pressure. A compressed air recirculation loop is often implemented with the above mentioned solution to prevent the pressure of the reserve air from exceeding a desired threshold, above which the reserve pressure may adversely affect the performance of the engine or even result in engine damage.
An example of a compressed air recirculation loop can be found in U.S. Pat. No. 6,318,085 (the '085 patent) issued to Torna et al. on Nov. 20, 2001. The compressed air recirculation loop disclosed in the '085 patent is fluidly connected to an air intake of a compressor. In addition, the recirculation loop is fluidly connected to an engine inlet passage downstream of the compressor. The engine inlet passage includes a throttle valve for controlling the flow of air into the engine. Furthermore, a recirculation valve situated within the recirculation loop regulates the flow of pressurized air back to the intake of the compressor. A sensor situated downstream of the throttle valve senses the pressure of air entering the engine, while another sensor, associated with the throttle valve, senses the position of the throttle valve. The recirculation valve is actuated based on the pressure of the air entering the engine and the position of the throttle valve to maintain the pressure of the air entering the engine at a desired pressure.
Although the system disclosed in the '085 patent utilizes a compressed air recirculation loop, its effect on the transient response of the turbocharger may be limited. In particular the '085 system does not sense the boost pressure upstream of the throttle valve. This may allow the actual boost pressure to become less than a desired boost pressure. If the pressure becomes too low, there may not be enough reserve of pressurized air to meet the demands of an increased load acting on the engine.
The disclosed system is directed to overcoming one or more of the problems set forth above.